如何使用bash中的字符串值作为变量名

Question

Hopefully I can make it clear. I would like to create a filename out of different strings in bash . For example hmd.sh so h , m , d are different values (number 0..9 or letter aA..zZ ). So for example I want to convert

h=1 m=11 and d=12 to 1aA.sh. h=> 1, m=>a and d=>A 

To declare variables like

a01=1; a02=2 .. a09=9, a10=0; a11=a; a12=b and so on. h(1)=a01=1 m(11)=a11=a 

and

d(12)=a12=A.

To test it I wrote this:

#!/bin/bash
dd01="1"
aa="01"
bb="dd$aa"
echo $bb

But of course $bb is dd01 and not its value. How can I make $bb its value of 1?

Answer 1

Associative arrays make this kind of thing much more readable.

However your answer is "variable indirection"

$ echo $bb
dd01
$ echo ${!bb}
1

Do not listen to any advice suggesting eval -- you open yourself up to all kinds of code injection.

Answer 2

The only way to expand a variable inside another is in an array when the variable is enclosed in the key's brackets like [$var] .

You could store your values in an associative array, and reference them like so:

declare -A arr
arr[dd01]="1"
arr[aa]="01"
arr[bb]="dd${arr[aa]}"
echo ${arr[${arr[bb]}]}

Using arrays like this may be more convoluted for this example than referencing the variable name using ${!bb} syntax, but if you need to do this while keeping different sets of variables that may need to reference each other, creating an associative array may make more organizational sense.

Answer 3

I rewrote your code example as follows which gives you the value of 1 which is what you are trying to achieve.

#!/bin/bash
dd01="1"
aa="01"
bb="dd$aa"
echo $[$bb]

Answer 4

This did the trick:

#!/bin/bash
dd=1234567890aAbBcC
aa="11"
echo ${dd:(aa-1):1}

Appearantly 1 is the 0 position and aa can also be like 01 and still work!

Thank for all the advices.

I found my answer here:

http://tldp.org/LDP/abs/html/string-manipulation.html

Answer 5

This should do the job:

#!/bin/bash
dd01="1"
aa="01"
bb="dd$aa"
eval echo \$$bb

Answer 6

You can use the '$' operator to access the value of a variable. For example...

d = 'Hi'
e = ' there '
f = 'friend.'
foo = '$d$e$f'

This would cause the value of foo to be 'Hi there friend.'

Hope this helps.

Answer 7

Use eval :

#!/bin/bash
dd01="1"
aa="01"
eval bb=\$dd$aa
echo $bb

This script outputs the expected 1 .